The repair of a metal parent piece of equipment by the attachment of a metal replacement piece has been accomplished by various welding procedures. When welding by electron beams or laser beams is used to fasten the replacement piece to the parent piece, however, it has been discovered that the effectiveness of the weld may be limited by its depth. Beam welding to depths exceeding the width of the puddle produced, for example, may result in a surface undercut at the fusion zone interfaces. When this occurs, neither the fusion zone nor the adjacent parent metal heat-affected zones is likely to exhibit acceptable mechanical properties, and failure of the weld may orginate in one or more of these zones.
During the processes of beam, especially electron beam, welding, two metal pieces together, energy is distributed from the impingement point of the beam into the zone to be welded due to the thermal conductivity of the base material. If the energy density of the impinging beam is sufficiently high, energy is distributed into the weld zone by the direct transfer of electron beam energy from the penetrating beam. Although such electron beam welding processes have been employed effectively to join metal pieces of various shapes and sizes, they have not produced the failure free deep welds required to reliably join a large bulky metal replacement piece to an equally large or bulky metal parent piece. Electron beam welding techniques are particularly sensitive to cracks, cavities, and the presence of foreigh or nonhomogeneous material in the weld zone which effectively reduce the amount of heat energy available for the weld. In addition, the high vapor pressures required in the irradiated area to produce an effective deep penetration weld may also produce temperatures far above the melting point of the welded base material. As a result, base material may be lost or changed due to escaping vapor and spraying and blowhole formation, all of which weaken the weld. Further, beam welding typically leaves the metal in the weld zone in a state that requires both additional manual processing to strengthen the weld and careful inspection to insure that no weakened areas remain.
The prior art has proposed various beam welding processes intended to produce a reliable deep weld. For example, U.S. Pat. No. 3,417,223 to Steigerwald discloses an electron beam welding process for producing a deep weld free from cracks, voids and other irregularities wherein a preheated filler material is positioned relative to the weld and to an electron beam to partially intersect the beam so that the preheated filler can fill any voids or cracks. The use of a separately preheated filler material, although it may be effective, adds an additional process step and this increases both the cost and complexity of the beam welding process.
U.S. Pat. No. 4,644,127 to LaRocca discloses a beam welding procedure wherein pieces of metal to be welded together are joined in the presence of an additional powdered filler material applied after irradiation by a laser beam and wherein the weld zone can be post-heated to improve its aesthetic and mechanical characteristics. However, it is not suggested in this patent either that the powdered filler material could be eliminated or replaced or that the post-heating limits the application of the beam to an area of lesser penetration than that initially preheated to improve the properties of the metal. Moreover, although this method may be well suited to the welding of relatively shallow butt joints, it would be of limited utility in joining large, irregular masses which require deep welds.
Other beam welding methods for joining two metal pieces have been proposed in the prior art. U.S. Pat. Nos. 3,230,339 to Opitz et al. and 4,272,665 to Steigerwald are illustrative of such methods. Although these methods may be well suited to the formation of the butt joints required to join sheets or other relatively thin metal pieces wherein beam deflection across a gap and filler material supplied to a gap are easy to control, neither could be successfully applied to form the kind of deep weld required to attach a bulky, irregularly shaped replacement piece to a similarly configured patent piece.
The prior art, therefore, has failed to disclose a beam welding process suitable for attaching a bulky, irregularly shaped replacement piece to a correspondingly bulky, irregularly shaped parent piece that simultaneously prepares the weld area, creates the weld joint and then anneals and tempers the weld to optimize the mechanical characteristics of the weld, thus producing a secure permanent attachment between the replacement piece and the parent piece.